FIG. 4.

PQ responsiveness of SoxR mutant proteins studied by Northern blot analysis. Strain TN402 expressing the various mutated SoxR proteins was treated for 5 min with 100 μM PQ before total RNA was obtained. The RNA was electrophoresed and transferred by Northern blotting, the filters were hybridized with a soxS-specific probe, and RNA was quantified in a phosphorimager. (Top) Northern blots showing soxS mRNA levels. (Middle) The corresponding ethidium bromide-strained gels show 23S and 16S rRNA that served as loading controls. (Bottom) Quantification of soxS mRNA levels obtained in Northern blots. soxS mRNA was normalized to 16S rRNA levels and is reported relative to the amount obtained with wild-type (WT) SoxR (set at 100%). The results shown are from one of two independent experiments.